In many computer applications, control commands are entered in a statically defined form that is defined by the command language of the computer software. Inputs that do not correspond exactly to the specified command statements are not recognized or processed at all. The input can either be generated by entering a sequence of characters via the keyboard or by speaking a control command into a microphone that is connected to a speech recognition system. Regardless of how the control command is input, it is always necessary for the input/recognized control command to precisely correspond to a control command specified by the computer software.
U.S. Pat. No. 5,737,485 discloses a system for speech recognition in which feature extractors are provided, both downstream from a microphone for close-talking and downstream of a microphone system for distant-talking, said feature extractors forming a sequence of features from a sequence of phonetic sounds. The sequence of features of the captured close-talking and distant-talking information is sent to a neural network that is provided to establish correlations between distorted features and largely distortion-free features in a learning phase and then later, in the speech recognition phase, to replace distorted features with features that are largely distortion-free and are consistent with the learned knowledge before the features are sent to a speech recognition means. The disadvantage of this system is its inability to react dynamically to changes in the generation of the sounds. In addition, the recognition of unclearly spoken words is not improved by the system.
DE 198 04 603 discloses a speech recognition system that uses a phonetic sequence to generate a sequence of features in the form of test signals. These test signals are then compared with the lexical knowledge in the form of reference signals, whereby sequences of reference signals represent words that are obtained from a training signal. The purpose of this is to improve the speech recognition means by not only comparing the features in the form of the test signals with the thus learned vocabulary but also with learned combinations of sentence elements that are most likely to occur. This does not, however improve the accuracy of speech recognition in the case of unclearly pronounced words.